This invention relates to an ignition timing control system for an internal combustion engine.
The ignition timing of internal combustion engines is settled so as to maximize the efficiency of the engine with respect to the mode of operation thereof. It is generally desirable to settle the ignition timing so that the particular internal combustion engine approaches a minimum advance for the best torque which may be abbreviated to "MBT" as close as possible within the range in which knocking is not caused in the engine. However, ignition timing control systems previously equipped on internal combustion engines have been, in many causes, of the mechanical type and the ignition advance angle characteristics thereof have not been stable with respect to deviations of dimensions and secular changes of components involved. Therefore, the ignition timing has been actually settled to retrogress fairly behind an ignition time point giving the desirable advance angle characteristic in order to prevent the occurrence of knocking. In this case the engine deteriorates in efficiency. Also even though ignition timing control systems free from both deviations of dimensions and secular changes as described above would be employed, knocking occurring in an associated internal combustion engine depends upon an inlet air temperature and an inlet humidity of the engine and further upon an air fuel ratio thereof etc. Accordingly, if the ignition timing could be settled so as not to cause knocking in the engine in some mode of operation, there might be a fear that knocking would be caused in the engine in another mode of operation.
Therefore by sensing knocking and controlling the ignition timing to retard upon the occurrence of knocking, the ignition timing can be adjusted so that knocking is scarcely caused even though an error would be caused in the ignition advance angle characteristic due to the deviations as described above of mechanical apparatus and differences between the modes of operation. Knocking can be sensed according to any of methods of the measuring a pressure within the combustion chamber of internal combustion engines, the acceleration of vibrations of the engines, sound generated in the engine, etc. In actual motor vehicles the method of measuring an acceleration of vibration of an associated engine is most practical in view of a position where an acceleration sensor involved is mounted, the processing of signals etc. As the method of measuring the acceleration is responsive to a knock signal and simultaneously to vibrational noise signals, knocking has been detected by selecting the knock signal from the vibrational noise signals. However this measure has encountered the problems that in the low speed operation of internal combustion engines or the like the knock signal is low in level, knocking is erroneously detected with other noise signals thereby to control the ignition time point of the engine to either an erroneous time point on the retrogressing side thereof or an unstable time point.
Accordingly it is an object of the present invention to provide a new and improved ignition timing control system for an internal combustion engine making it possible to impart stable ignition time points to the engine to operate the latter with a good efficiency even in an operating range in which knocking is erroneously detected, by disabling the functions of controlling the ignition timing with a knock signal in the low speed mode of operation of the engine.
It is another object of the present invention to provide a new and improved ignition timing control system for an internal combustion engine making it possible to impart stable ignition timing points to the engine to ensure the starting characteristics of the engine during the starting thereof in which knocking is erroneously detected, by disabling the function of controlling ignition timing with a knock signal in the low speed mode of operation of the engine and more particularly during the start thereof.